For me, he stamped the page preceding the visa double-page, and he took some effort to open specifically that page, so it seems intentional (that was in April/May 2016).
You shouldn't be too worried about saving space, most border agents stamp across whatever is there without caring once the passport gets kind of full, and you can always get a new one.
I have not heard of any case where there were immigration issues because the passport was 'full'.
travel.stackexchange.com/users/37993/Aganju
I’ll admit that ‘two’ is a small number of data points but it is still larger than zero, so here goes:
I entered (and exited) Russia twice.
Once by train from Helsinki (inbound on the Saint Petersburg train, return on the Moscow train) and once from Belarus with detours to Helsinki (inbound coming from Prague, returning on a Saint Petersburg–Helsinki train).
In all four occasions (one of which being Belarusian immigration) the entry and exit stamps were stamped onto the visa.
It makes sense because the visa allocate space for the stamps if you look at it properly.
travel.stackexchange.com/users/43483/Jan
I've travel a lot from Russia, and I saw many foreigners going through the border, and I can say that border guards usually are trying to save the place, stamping the nearest to the visa page in passport.
Stamps on Russian borders usually are small enough to get two on one line of the page, so I think that you wouldn't lose much space there, but still, probably, one page will be stamped.
travel.stackexchange.com/users/19/VMAtm
UPDATE:
On the Allegro train, by default, they placed the entry stamp on a separate page
- I saw it happen to a Spanish citizen who was checked before me.
However, I politely asked the officer, in broken Russian, to stamp the visa instead ("pozhaluista shtamp na visa, niet drugoj stranitsa"), and she was perfectly OK doing so.
Same thing when exiting for Kazakhstan.
Below is a picture of my visa with stamps
travel.stackexchange.com/users/39782/Crazydre
I have three single entry visas (newest is from 2016), traveling with train from Helsinki and with plane.
In each case, entry stamp was placed on the next page, and exit stamp was placed on the visa.
travel.stackexchange.com/users/None/
I think it matters if you have a single or multiple entry visa I have travelled 4 times: 2010-
Single visa, Both stamped on the visa
2015- Double Entry, First entry and Last Exit only stamped on visa 2016- Single Entry-
Both on visa 2016- Double-
Not on visa
travel.stackexchange.com/users/52785/Andre Bouzid
I have travelled to/from Russia more than a dozen times in the last few years - on USA passport and on British passport.
Every single time the stamp went onto the visa itself.
travel.stackexchange.com/users/14128/Aleks G
I'm aware both scenarios are common, but which is most common? Does anyone have any experience? Does it vary between different border crossings?  I'd much rather they stamped the visa, so that no additional space is wasted.  Like in this Image  http://img.click.in/classifieds/images/148/23_2_2014_16_15_24_hfcosv8748i9js0qj2hjmu64a4_1k2hq73s5y.jpg
Do Russian border guards usually stamp on the visa, or on a separate page?
travel.stackexchange.com
<visas><russia><passport-stamps>
travel.stackexchange.com/questions/68646
travel.stackexchange.com/users/39782/Crazydre
The entry stamp usually goes on the page next to the visa double-page, and the exit stamp on the visa itself. Once the passport gets quite full, agents usually stamp wherever there is space, or you can just get a new passport. There appears to be no consensus about where Russian immigration officers place visa stamps. Sometimes it is on the visa and sometimes it is on a nearby page.
There appears to be no consensus about where Russian immigration officers place visa stamps. Sometimes it is on the visa and sometimes it is on a nearby page.