Hi qwinkan:
Can't say for sure, but you said Yahoo Beta. "Beta" means that the software is currently under the debugging stage (finding errors in code, design, etc...). Creating a piece of software is very extensive, and goes through many stages of development. The version you have right now is a newer version, which may not be fully complete/functional. If you use a stable version of it, you shouldn't have a problem, then once maybe the beta version is considered stable, switch to that. Since you switched, you shouldn't have a problem with it. I would wait for a stable release, then upgrade
Also, have you taken a look at AdiumX? You can add a Yahoo account, even a Yahoo Japan! account if you want. It's pretty nifty. If you have other services like Gmail, ICQ, etc -- you can have it all in one program. It has never crashed on me, so I'm assuming the same for you.
- Pratik