Is this a strange sentence?
Z have been supporting and are still supporting the current uk dates for X.
"Have been supporting" is present perfect continuous that means the action is still going on , so there is no need to add "are still supporting". Or maybe the action stopped recently, started again after a little break and is still going on in that case I understand "are still supporting".
The usage is not unusual.
Despite there technically being a degree of redundancy in the meaning, people would read it and know what it meant without feeling that it was in any way forced or unusual.
On reflection it is likely that the writer has written in this way to ensure that there is no doubt either re wht they have been doing or what they are doing now. I they simply wrote "Z have been supporting the current uk dates for X" there would be a reasonable possibility that some people may wonder if something like " ... until recently, but no longer do." may be inferred.
The " ... we have been ..." construct does not carry a clear message to the reader that the action is ongoing, regardless of whether the formal usage indicates that this should be the case.
It would not be unusual for people to use something like "We have been supporting xxx | until now, but ..." or evgen "We have been supporting xxx, but ...". Because the "shadow" of this sort of addition is present in the phrase, adding something to indicate ongoing support is a "safe" action to ensure that there is no understanding.
Examples:
"We have been supporting Richard's campaign, but now find out that he beats his wife. [Implied: And so we no longer do].
'Why do you not include Oxfam in your charity giving?' "We always give to a wide range of charities. We have been supporting Oxfam for the past 45 years." [Implication: We have chosen to give our money elsewhere instead.]
The same answer as above to "Do you give to Oxfam?" may mean they still do so and are proud of it OR may mean that they have now stopped doing so but do not want to make the fact obvious or that they still do so [!}.
Z have been supporting and are still supporting the current uk dates for X.
We usually use the present perfect continuous for an action over a period of time leading up to the present time - the action is still ongoing.
Besides, we can also use it to talk about an action which ends just before the present. For example, I have been swimming, That's why my hair is wet.
I think the present perfect continuous used in the sentence conveys the latter sense. The use of the present perfect continuous and then the use of the present continuous put emphasis on the ongoing action of supporting.
