SNMP port speed bug on GS308T 1.0.5.5 firmware

Hello everybody,

I think there's something's wrong with SNMP on 1.0.5.5 firmware for GS308T switches.

I check ports speed and value is always "1000000000" , even if the port is down.

For example, only port 8 is up on my switch but : 

With MIB : 

IF-MIB::ifSpeed.1 = Gauge32: 1000000000
IF-MIB::ifSpeed.2 = Gauge32: 1000000000
IF-MIB::ifSpeed.3 = Gauge32: 1000000000
IF-MIB::ifSpeed.4 = Gauge32: 1000000000
IF-MIB::ifSpeed.5 = Gauge32: 1000000000
IF-MIB::ifSpeed.6 = Gauge32: 1000000000
IF-MIB::ifSpeed.7 = Gauge32: 1000000000
IF-MIB::ifSpeed.8 = Gauge32: 1000000000

With OID : 

.1.3.6.1.2.1.2.2.1.5.1 = Gauge32: 1000000000
.1.3.6.1.2.1.2.2.1.5.2 = Gauge32: 1000000000
.1.3.6.1.2.1.2.2.1.5.3 = Gauge32: 1000000000
.1.3.6.1.2.1.2.2.1.5.4 = Gauge32: 1000000000
.1.3.6.1.2.1.2.2.1.5.5 = Gauge32: 1000000000
.1.3.6.1.2.1.2.2.1.5.6 = Gauge32: 1000000000
.1.3.6.1.2.1.2.2.1.5.7 = Gauge32: 1000000000
.1.3.6.1.2.1.2.2.1.5.8 = Gauge32: 1000000000

In WebGUI it's not the case (see attached picture).

Am I missing something or is there really a bug in this firmware ? 

Thanks for your help.