Upon rejoining a channel and the logs are reloaded into the window buffer it's not respecting the line amount set in the window buffer setting, is this by design?

Only time a window ever reaches the window buffer setting is when the channel has accumulated enough messages after you've joined it.

I have buffer lines set to 5000 but it only loads around 1000 when I rejoin a channel.

Is this the intended behavior, or a bug? Please clarify.

Thanks.

Thanks for your bug report. The limit of reloading only 500 lines was implemented in mIRC v6.32. If I recall correctly, the reason was that users were reporting excessive memory usage when reloading as many lines as specified in the buffer size, whose maximum is 50000, with many windows open. The limit of 500 lines was later extended to 1000 lines, as that was considered arbitrarily sufficient when reloading for most users, in as much as 50000 lines is also an arbitrary maximum.

Since my initial post I've found I can automate the /loadbuf command on select channels upon joining, thanks.