Backlight lights up based on SIP session expire

[CFortC]

I have this problem with both a T48G and a T48S each running respective most recent firmware. I've re-tried on every earlier firmware version still downloadable, with no resolution. I've factory reset and reconfigured, etc. with no resolution.

The issue is that the dimmed (or power-saved off) backlight will return to ON status whenever the SIP server registration expires (account.X.sip_server.1.expires) . For example, if that is set to 300s, then the backlight returns to ON every five minutes. This is quite annoying over time.

MAJOR additional information: with just one SIP account registered, this problem does NOT occur. However, my normal setup has two distinct SIP accounts. The enabling of the second account also activates this problem.

In researching the issue, I noticed that a similar problem was reported in the "T2xP Series" forum as thread "T22P display backlight lights up every 2 mins". That was around 2014 and that issue was eventually fixed with a firmware update. For the T22P issue, the number of SIP accounts registered wasn't specified. Perhaps the T22P user had only one account registered. I only mention this T22P problem because of the similar symptoms to what I'm seeing today with my T48G and T48S.

Any others seeing this issue? Any different configuration I need to set to allow two SIP accounts to run the backlight properly? Firmware Fix possible? (T48G is end-of-life, so access to an OLD firmware without this problem would also be acceptable.)

Thanks in advance for any help.