Well, I have a standard version of mIRC... almost standard - I configured it a little bit. I include it here, omitting irrelevant lines:
There isn't always possible to reproduce it, but I realized that if it happened one, there are more changes it will hapen again in the close future. And I think that it happens less often in mIRC 6.1 (I'm not sure, however).
I also add an excrept from one of my logs. Please ignore the language (Romanian), but observe the effect I was talking about:
<GrayShade> bine... am mai luat articole de pe net intr timp
<TheCreeep> ok, merci
-> [gata........] PING
-> [TheCreeep] PING
<GrayShade> te-ai uitat prin ele?
P. S.: I thought my English was better...