I have heard the same. If that happens, they will not give you the opportunity to return to Canada and continue the application. They will ask you to prove that you have been residing in Canada since you applied. If you fail to do that, they will cancel it.
In Canada, vacation is 2-3 weeks. Anything above that is something else. You could argue that residing in Canada for tax purposes as well as health care is anything more than 6 month a year but immigration will have already cancelled your application at that point and it will delay your case by months and there is no guarantee that you would win that appeal even if you try it.
Therefore, if you want to visit your spouse, make sure you go for no more than 3 weeks and make sure someone is checking your mail and messages while you are gone. Some people have gone to stay with their spouse after stage 1 and gotten away with it. Others were caught and lost their applications. Personally, I would not take the risk. You do not lose your PR if you lose your application as long as you meet the RO but you would have to return to Canada and re-do the sponsorship application from scratch.