L.R.
I think you are right. I just experienced the same thing with my 6 month old. I am convinced it is the excitement of being able to get around on her own... and prior to the crawling I had been putting her in a "Sleep Sack" and nursing her then rocking her to sleep and laying her down.. once she started crawling she would immediatly wake up upon placement in her crib... and start crawling and crying. This went on for about a week and a half... we were near crisis. Obviously what had worked wasn't anymore so I did the exact opposite of what I would normally do...
I tried waiting until she seemed sleepy rather than nursing or rocking her to sleep, instead we took a bath together and I dressed her in a nightie then held her in the dark to help settle her down taking nice deep breaths and yawning a few times(with her night light on and soft ambient sleep music playing on repeat) then put her in her crib with her favorite blanket still awake, kissing her and telling her night night... she would fuss when I walked out and begin to scream.. I checked on her every 5 min... kept it brief, didn't pick her up like she wanted me to do, but let her know I'd be there if she needed me... it took about 3 visits...she was fine just didn't want to go to bed...then suddenly there was silence... I was nervous because I had never left her in bed with anything before, but when I went in to check on her one last time she was sound asleep. The blanket seems to be key... it is now working for naps too... but like everything... well see how long this works lol.